There are prior art means for controlling a group of electric motors (control stations) including a plurality of contactors, intermediate electromagnetic relays and other switching elements, the number of which is dictated by the number of electric motors to be controlled. Such means are complicated, cumbersome and of low reliability.
The known means are particularly disadvantageous when used in the equipment for controlling the energization of machines operated in mines, in dangerously explosive environment. To comply the necessary measures for safe operation under these conditions, a number of special requirements are to be met, and among them is checking of the insulation of an electric circuit connecting the processing equipment and the supply mains. Such checking is to be carried out before the circuit is energized.
To meet such requirements, it is necessary to use special check meters in every set of equipment for controlling an individual power actuated member.
Known in the art is a high voltage switchgear (USSR Inventor's Certificate No. 320846) which includes a fixed panel with contacts arranged around a circumference, an electromagnetic drive, whose actuating element rotates about an axis passing through the center of said circumference perpendicularly to the contact plane and reciprocates along said axis. The switchgear additionally includes a switch unit rigidly connected with the actuating element of the electromagnetic drive for switching over the contacts, when the electromagnetic drive comes into operation. In this switchgear, an electromagnet armature which is an actuating element is provided with a cam in the form of a sleeve having a saw-like groove variable in depth and made around its cylindrical surface to accomodate a pin fixed to the electromagnet casing for running in said groove.
As the electromagnet coil is energized, the armature is attracted thereinto. The pin moves along the saw-like groove of the cam and, in acting thereupon, turns the armature together with the switch element through an angle corresponding to the pich of the saw-like groove.
However, the above switchgear may be used only for a sequential switching of circuits to be energized and is unsuitable for a selective switching of individual power actuated members.
In addition, the above switchgear is unfit for performing such a switching operation, which enables all the circuits or a part of them to be energized simultaneously.
It should be noted that the switchgear being described is provided with no means for protecting the circuits in case the power supply is interrupted.
Thus, the described switchgear may be used for switching power circuits only in combination with auxiliary switch elements.
Therefore, when the above switchgear is employed for controlling a plurality of power actuated members it is impossible to substantially reduce the number of relays and other auxiliary switch elements.